Grand-design spiral galaxy

A spiral galaxy with two or more prominent, well-organized arms forming a coherent pattern that extends from its central region. Its arms are more clearly defined than the fragmented arms of a flocculent spiral.

Density wave theory: A theory that explains spiral structure as waves of enhanced density moving through a galactic disk. It accounts for arms that remain coherent even as stars and gas move through them.
M51: A nearby interacting pair of galaxies, including the grand-design spiral known as the Whirlpool Galaxy. Its striking two-arm pattern is a classic example of a grand-design spiral.
Flocculent spiral galaxy: A spiral galaxy whose arms are fragmented into patchy, irregular segments rather than forming a coherent pattern. Its fragmented arms provide the clearest contrast with grand-design structure.
Hubble sequence: A classification scheme that arranges galaxies by visible morphology, including ellipticals, lenticulars, and spirals. It places spiral structure within the broader visual classification of galaxies.
Differential rotation: Rotation in which different parts of a system have different angular velocities. A galaxy's faster inner rotation would wind up material arms without a mechanism that sustains their pattern.
M81: A nearby spiral galaxy in the constellation Ursa Major with a prominent two-arm structure. Its well-defined arms make it another prominent example of the class.
Multi-arm spiral galaxy: A spiral galaxy with several arms or arm segments rather than a dominant, coherent two-arm pattern. Its multiple features differ from the prominent, organized arms defining this class.
Galaxy morphology: The study and classification of galaxies by their visible shapes and structural features. Arm coherence is one morphological feature used to describe spiral galaxies.
Swing amplification: A process that amplifies disturbances in a differentially rotating galactic disk into spiral-shaped patterns. It can strengthen spiral features from small disturbances in a disk.
NGC 1300: A barred spiral galaxy in the Eridanus constellation with a large, well-defined spiral pattern. Its organized arms extend from the ends of a prominent central bar.

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